Waterproof structure for electronic unit

ABSTRACT

A waterproof structure for an electronic unit includes a sub-case that defines an accommodating portion that accommodates a first terminal, and has a cable guiding hole that communicates with the accommodating portion. A potting resin filled in the accommodating portion is also filled in a space between a cable and the cable guiding hole. The cable includes a first sheath that covers a conductor and is made of a first resin material, and a second sheath that covers the first sheath. The second sheath and the potting resin are made of a second resin material that is different from the first resin material.

INCORPORATION BY REFERENCE/RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2012-045597 filed on Mar. 1, 2012 the disclosure of which, including thespecification, drawings and abstract, is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a waterproof structure for an electronic unit.

2. Discussion of Background

Japanese Patent Application Publication No. 11-26065 (JP 11-26065 A)describes a waterproof structure for an electronic unit, which isconfigured by filling a case, into which a cable is drawn through acable guiding hole, with a potting resin.

A sheath that constitutes an outer sheath of the cable, and the pottingresin are made of different resin materials. Therefore, adhesion betweenthe potting resin after curing and the sheath of the cable is notsufficiently high, which may reduce the waterproof performance.

SUMMARY OF THE INVENTION

The invention provides a waterproof structure for an electronic unit,which improves the waterproof performance of a cable guiding hole.

According to a feature of an example of the invention, a waterproofstructure for an electronic unit, includes: a case that defines anaccommodating portion that accommodates a first terminal, and that has acable guiding hole that communicates with the accommodating portion; acable that has a conductor connected to a second terminal to which thefirst terminal is connected, a first sheath that covers the conductor,and a second sheath that covers the first sheath, the cable being passedthrough the cable guiding hole and drawn into the accommodating portion;and a potting resin that is filled in the accommodating portion and aspace between the cable and the cable guiding hole, the first sheath ismade of a first resin material, and the second sheath and the pottingresin are made of a second resin material that is different from thefirst resin material.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description of exampleembodiment with reference to the accompanying drawings, wherein likenumerals are used to represent like elements and wherein:

FIG. 1 is a schematic diagram showing the configuration of an electricpower steering system to which a waterproof structure for an electronicunit according to an embodiment of the invention is applied;

FIG. 2 is a sectional view of a main part of the waterproof structurefor the electronic unit;

FIG. 3 is a perspective view mainly showing a sub-case body of theelectronic unit;

FIG. 4 is a side view of the waterproof structure for the electronicunit;

FIG. 5 is an enlarged sectional view of the main part of the waterproofstructure for the electronic unit;

FIG. 6 is a schematic front view of an insulator of a connector that isattached to the sub-case body;

FIG. 7 is a sectional view of a cable passed through a cable guidinghole; and

FIG. 8 is a sectional view showing an end portion of a second sheath ofthe cable and its surroundings.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiment of the invention will be described withreference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the configuration of an electricpower steering system 1 that serves as a vehicle steering system towhich a waterproof structure for an electronic unit according to anembodiment of the invention is applied. The electric power steeringsystem 1 includes a steering wheel 2 that serves as a steering member, asteered mechanism 4 that steer steered wheels 3 in response to therotation of the steering wheel 2, and a steering assist mechanism 5 forassisting a driver in performing a steering operation. The steeringwheel 2 and the steered mechanism 4 are mechanically connected to eachother via a steering shaft 6 and an intermediate shaft 7.

In the present embodiment, description will be provided on an example inwhich the steering assist mechanism 5 applies an assist force (steeringassist force) to the steering shaft 6. However, the invention may beapplied to a structure where the steering assist mechanism 5 applies anassist force to a pinion shaft (described later), or a structure wherethe steering assist mechanism 5 applies an assist force to a rack shaft(described later). The steering shaft 6 includes an input shaft 8connected to the steering wheel 2, and an output shaft 9 connected tothe intermediate shaft 7. The input shaft 8 and the output shaft 9 arecoaxially connected to each other through a torsion bar 10 so as to berotatable relative to each other.

A torque sensor 11 arranged around the steering shaft 6 detects asteering torque input into the steering wheel 2, based on a relativerotational displacement between the input shaft 8 and the output shaft9. A torque detection result obtained by the torque sensor 11 is inputinto an ECU (electronic control unit) 12 that may function as anelectronic unit. A vehicle speed detection result obtained by a vehiclespeed sensor 22 is also input into the ECU 12. The intermediate shaft 7connects the steering shaft 6 and the steered mechanism 4 to each other,

The steered mechanism 4 is formed of a rack-and-pinion mechanism thatincludes a pinion shaft 13 and a rack shaft 14 that serves as a steeredshaft. The steered wheels 3 are connected to respective end portions ofthe rack shaft 14 via tie rods 15 and knuckle arms (not shown). Thepinion shaft 13 is connected to the intermediate shaft 7. The pinionshaft 13 rotates in accordance with a steering operation of the steeringwheel 2. A pinion 16 is provided at a distal end (lower end in FIG. 1)of the pinion shaft 13.

The rack shaft 14 extends linearly in the lateral direction of avehicle. In an intermediate portion of the rack shaft 14, a rack 17 thatmeshes with the pinion 16 is formed. With the pinion 16 and the rack 17,the rotation of the pinion shaft 13 is converted into an axial movementof the rack shaft 14. By moving the rack shaft 14 in the axialdirection, the steered wheels 3 are steered.

As the steering wheel 2 is steered (rotated), the rotation istransmitted to the pinion shaft 13 via the steering shaft 6 and theintermediate shaft 7. Then, the rotation of the pinion shaft 13 isconverted into an axial movement of the rack shaft 14 by the pinion 16and the rack 17. Thus, the steered wheels 3 are steered. The steeringassist mechanism 5 includes an electric motor 18 for steering assist,and a speed reduction mechanism 19 for transmitting an output torque ofthe electric motor 18 to the steered mechanism 4. The speed reductionmechanism 19 includes a worm shaft 20 that serves as a drive gear (inputshaft) to which a driving force of the electric motor 18 is input, and aworm wheel 21 that serves as a driven gear that meshes with the wormshaft 20.

The worm shaft 20 is connected to an output shaft (not shown) of theelectric motor 18 via a joint (not shown). The worm shaft 20 is rotatedby the electric motor 18. The worm wheel 21 is connected to the steeringshaft 6 so as to be rotatable with the steering shaft 6. As the electricmotor 18 rotates the worm shaft 20, the worm wheel 21 is rotated by theworm shaft 20, and the worm wheel 21 and the steering shaft 6 arerotated together with each other. Thus, a steering assist force istransmitted to the steering shaft 6.

The electric motor 18 is controlled by the ECU 12. The ECU 12 controlsthe electric motor 18 based on the torque detection result obtained fromthe torque sensor 11, the vehicle speed detection result obtained fromthe vehicle speed sensor 22, and the like. Specifically, the ECU 12determines a target assist amount with the use of a map that stores thecorrelation between a torque and a target assist amount for each vehiclespeed. Then, the ECU 12 controls the electric motor 18 such that anassist force generated by the electric motor 18 approaches the targetassist amount.

FIG. 2 is a sectional view of a waterproof structure A for an electronicunit, The ECU 12 is provided with a main case 24 and a sub-case 25. Themain case 24 accommodates a substrate 23 and other electronic components(not shown), and is made of, for example, an aluminum alloy. Thesub-case 25 is fixedly fitted to the main case 24, and is made of, forexample, a synthetic resin.

As shown in FIG. 3, the sub-case 25 (a sub-case body 30 described later)accommodates a group of terminals 26 and first terminals 27A, 27B, 27C(collectively referred to as “first terminals 27” where appropriate).For example, terminals (not shown) provided at ends of wires, throughwhich signals from the torque sensor 11 are input into the ECU 12, areconnected to the terminals 26. A terminal provided at an end of a wirethat transmits signals through an integrated ECU and a controller areanetwork (CAN) on the vehicle side, a terminal provided at an end of awire connected to a battery, and a terminal provided at an end of a wireconnected to the earth are connected to the first terminals 27A, 27B,27C, respectively.

As shown in FIG. 4 which is a side view, the sub-case 25 is formed byassembling together the sub-case body 30 and a connector 32 that has awall portion 31 that forms part of an outer wall of the sub-case 25. Thesub-case body 30 has: a bottom plate 35 that covers, from the inside, amounting hole 34 formed in an outer wall 33 of the main case 24 as shownin FIG. 2 and FIG. 4; a first wall 36 and a second wall 37 (see FIG. 3)that extend from the bottom plate 35 outward (upward in FIG. 2) of themain case 24 through the mounting hole 34; a third wall 38 that extendsfrom the bottom plate 35 and has an opening 38 a; and a fourth wall 39that extends from the bottom plate 35 and has an opening 39 a.

As shown in FIG. 2, the waterproof structure A for an electronic unitincludes: the sub-case 25 that defines an accommodating portion 40 thataccommodates, for example, the first terminals 27, and has cable guidingholes 41 that communicate with the accommodating portion 40; cables 42drawn into the sub-case 25 through the cable guiding holes 41; and apotting resin 43 filled into the sub-case 25 and spaces between thecables 42 and the cable guiding holes 41. The potting resin 43 is filledinto the sub-case 25 and the spaces in a liquid state, and then cured.

Main features of the present embodiment are that each cable 42 includesa conductor 45 that is connected to a second terminal 44A connected to acorresponding one of the first terminal 27, a first sheath 46 thatcovers the conductor 45, and a sleeve-like second sheath 47 that coversthe first sheath 46, and that the space between (the second sheath 47of) the cable 42 and the cable guiding hole 41 is filled with thepotting resin 43. In other words, the second sheath 47 is molded by thepotting resin 43 within the cable guiding hole 41. The first sheath 46is made of a first resin material (for example, polyethylene), and thesecond sheath 47 and the potting resin 43 are made of a second resinmaterial (for example, polyurethane) that is different from the firstresin material.

As shown in FIG. 4, the sub-case body 30 covers the mounting hole 34,and also partially projects from the mounting hole 34. The firstterminals 27A to 27C (only the first terminal 27A is shown in FIG. 2)that extend from the substrate 23 arranged in the main case 24 passthrough the bottom plate 35 of the sub-case 25 and are accommodated inthe accommodating portion 40. An upper face 35 a of the bottom plate 35forms a reference plane BP that is horizontally placed during resinpotting where the potting resin in a liquid state is injected into theaccommodating portion 40. The substrate 23 is held in a recessed portion35 b formed in a lower face of the bottom plate 35. One end of each ofthe first terminals 27A, 27B, 27C is connected to a conductive part ofthe substrate 23 within the main case 24.

As shown in FIG. 4, the connector 32 includes an insulator 48 attachedto the sub-case 25, and the second terminals 44A, 44B, 44C that aresupported by the insulator 48 and connected to the first terminals 27A,27B, 27C, respectively. Each of the second terminals 44A, 44B, 44C has aportion to which the conductor 45 of a corresponding one of the cables42 is connected, and a portion to which a corresponding on of the firstterminals 27A, 27B, and 27C is connected. These portions are orthogonalto each other.

The insulator 48 includes the wall portion 31 that is fitted in aninsertion groove 60 (see also FIG. 3) formed in the sub-case body 30,tubular cable guiding portions 49 connected to the wall portion 31, anda terminal holding portion 50 that extends from the wall portion 31,that is provided on the opposite side of the wall portion 31 from thecable guiding portions 49, and that supports the second terminals 44A to44C. As shown in FIG. 2, the wall portion 31 forms part of the wall ofthe sub-case 25 and defines part of the accommodating portion 40 whenthe wall portion 31 is fitted to the sub-case body 30. The cable guidingportions 49 define the cable guiding holes 41 through which the cables42 are drawn into the sub-case 25.

As shown in FIG. 5 and FIG. 6, an inner periphery 41 a of an inlet ofthe cable guiding hole 41 is provided with at least one annular sealingprojection 51 that closely contacts the outer periphery of acorresponding one of the cables 42 (the outer periphery corresponds toan outer periphery 47 a of the second sheath 47). In addition, as shownin FIG. 5, FIG. 6 and FIG. 7, the inner periphery 41 a of the cableguiding hole 41 is provided with a plurality of centering projections 52(in the present embodiment, the centering projections 52 are formed atthree positions in the circumferential direction and two positions inthe axial direction, that is, six centering projections 52 are formed intotal). The centering projections 52 are formed at equal intervals inthe circumferential direction of the inner periphery 41 a of the cableguiding hole 41. When the centering projections 52 contact the outerperiphery of the cable 42 (the outer periphery 47 a of the second sheath47), the centering projections 52 function to perform centering of thecable guiding hole 41 and the cable 42.

As shown in FIG. 4 and FIG. 8, an end portion 471 of the second sheath47 of each cable 42 (an end portion 471 of the second sheath 47, whichis on the outer side of the sub-case 25), which is drawn out from theinsulator 48, is covered together with the first sheath 46, by a heatshrinkable tube 53. A space between one end 531 of the heat shrinkabletube 53 and the second sheath 47, and a space between the other end 532of the heat shrinkable tube 53 and the first sheath 46 are sealed by ahot melt adhesive 54.

As shown in FIG. 5, FIG. 6, and FIG. 7, each cable guiding hole 41communicates, at a portion in the circumferential direction (upperportion), with a corresponding on of vertical grooves 55, and aninternal upper face 55 a of the vertical groove 55 is sloped such thatthe diameter of the vertical groove 55 increases toward theaccommodating portion 40. Thus, when the potting resin 43 is supplied ina liquid state, it is possible to purge the air remaining in the cableguiding hole 41 from the cable guiding hole 41 through the verticalgroove 55.

According to the present embodiment, the first sheath 46 that covers theconductor 45 of the cable 42 and is made of the first resin material iscovered with the second sheath 47, and the second sheath 47 and thepotting resin 43 are made of the same second resin material. Therefore,adhesion between the potting resin 43 and the outer periphery of thecable 42 (the outer periphery 47 a of the second sheath 47) isremarkably improved in the cable guiding hole 41. As a result, it ispossible to ensure high waterproof performance.

Because the end portion 471 of the second sheath 47 of the cable 42,which is on the outer side of the sub-case 25, is covered together withthe first sheath 46 by the heat shrinkable tube 53, it is possible toreliably prevent water from entering the inner side of the second sheath47. Thus, the waterproof performance is further improved. When thesecond resin material is polyurethane, the second material is able tofulfill a sufficient function as an outer sheath of the cable 42 and thepotting resin 43.

When the first resin material is polyethylene, performances as an innersheath of the cable 42, such as the strength and the insulationperformance, are enhanced, and the cost is reduced. The centeringprojections 52 that project from the inner periphery 41 a of the cableguiding hole 41 contact the outer periphery of the cable 42 (the outerperiphery 47 a of the second sheath 47) to perform centering of thecable guiding hole 41 and the cable 42. Thus, clearances having auniform size are formed on the outer periphery of the cable 42, and theclearances are filled with the potting resin 43. Therefore, the sealingperformance is remarkably improved.

The sealing projections 51 provided at the inlet of each cable guidinghole 41 closely contact the outer periphery of the cable 42 (the outerperiphery 47 a of the second sheath 47). Therefore, it is possible tosuppress leakage of the potting resin that has entered the cable guidinghole 41 in a liquid state before curing. In addition, the space betweenthe one end 531 of the heat shrinkable tube 53 and the second sheath 47,and the space between the other end 532 of the heat shrinkable tube andthe first sheath 46 are sealed by the hot melt adhesive 54. Therefore,the sealing performance between the heat shrinkable tube 53 and each ofthe sheaths 46, 47 is significantly improved.

The invention is not limited to the above-described embodiment, andvarious changes may be made to the above-described embodiment within thescope of the appended claims.

What is claimed is:
 1. A waterproof structure for an electronic unit,comprising: a case that defines an accommodating portion thataccommodates a first terminal, and that has a cable guiding hole thatcommunicates with the accommodating portion; a cable that has aconductor connected to a second terminal to which the first terminal isconnected, a first sheath that covers the conductor, and a second sheaththat covers the first sheath, the cable being passed through the cableguiding hole and drawn into the accommodating portion; and a pottingresin that is filled in the accommodating portion and a space betweenthe cable and the cable guiding hole, wherein the first sheath is madeof a first resin material, and the second sheath and the potting resinare made of a second resin material that is different from the firstresin material.
 2. The waterproof structure for an electronic unitaccording to claim 1, further comprising a heat shrinkable tube thatcovers an end portion of the second sheath, which is on an outer side ofthe case, and the first sheath together with each other.
 3. Thewaterproof structure for an electronic unit according to claim 1,wherein the second resin material is polyurethane.
 4. The waterproofstructure for an electronic unit according to claim 1, wherein the firstresin material is polyethylene.
 5. The waterproof structure for anelectronic unit according to claim 1, further comprising a plurality ofcentering projections that project from an inner periphery of the cableguiding hole and contact an outer periphery of the cable.
 6. Thewaterproof structure for an electronic unit according to claim 1,further comprising at least one annular sealing projection that isarranged at an inlet of the cable guiding hole, and that closelycontacts the outer periphery of the cable.
 7. The waterproof structurefor an electronic unit according to claim 2, wherein a space between oneend of the heat shrinkable tube and the second sheath, and a spacebetween the other end of the heat shrinkable tube and the first sheathare sealed by a hot melt adhesive.